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image viewer: add quick guide describing how to add image decoder. also improve comments.

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git-svn-id: svn://svn.rockbox.org/rockbox/trunk@29066 a1c6a512-1295-4272-9138-f99709370657
This commit is contained in:
Teruaki Kawashima 2011-01-16 12:45:11 +00:00
parent 5c09844d54
commit 62207228f7
2 changed files with 50 additions and 8 deletions
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21
apps/plugins/imageviewer/imageviewer.h
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@ -469,19 +469,24 @@ struct imgdec_api {
/* functions need to be implemented in each image decoders. */
struct image_decoder {
/* if unscaled image can be always displayed when there isn't enough memory
* for resized image. e.g. when using native format to store image. */
/* set true if unscaled image can be always displayed even when there isn't
* enough memory for resized image. e.g. when using native format to store
* image. */
const bool unscaled_avail;
/* return needed size of buffer to store downscaled image by ds */
/* return needed size of buffer to store downscaled image by ds.
* this is used to calculate min downscale. */
int (*img_mem)(int ds);
/* load image from filename. set width and height of info properly. also, set
* buf_size to remaining size of buf after load image. it is used to caluclate
* min downscale. */
/* load image from filename. use the passed buffer to store loaded, decoded
* or resized image later, so save it to local variables if needed.
* set width and height of info properly. also, set buf_size to remaining
* size of buf after load image. it is used to calculate min downscale.
* return PLUGIN_ERROR for error. ui will skip to next image. */
int (*load_image)(char *filename, struct image_info *info,
unsigned char *buf, ssize_t *buf_size);
/* downscale loaded image by ds. note that buf to store reszied image is not
* provided. return PLUGIN_ERROR for error. ui will skip to next image. */
/* downscale loaded image by ds. use the buffer passed to load_image to
* reszie image and/or store resized image.
* return PLUGIN_ERROR for error. ui will skip to next image. */
int (*get_image)(struct image_info *info, int ds);
/* draw part of image */
void (*draw_image_rect)(struct image_info *info,

37
apps/plugins/imageviewer/readme.txt Normal file
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@ -0,0 +1,37 @@
this document describes how to add new image decoder.
1. create a directory which name is your image decoder's name and put source files
under the directory.
'const struct image_decoder image_decoder' and 'IMGDEC_HEADER' must be declared in
one of your source files.
see imageviewer.h for the detail of struct image_decoder.
2. add the directory name to apps/plugins/imageviewer/SUBDIR so that the decoder
is built.
if the decoder is supported by particular targets, surround it with #if directive.
e.g. if the decoder supports color LCD targets only,
#ifdef HAVE_LCD_COLOR
bmp
#endif
3. append appropriate entry to enum image_type in image_decoder.h, decoder_names
and ext_list in image_decoder.c so that the imageviewer plugin can recognize
the decoder.
if the decoder is supported by particular targets, surround them with same #if
directive in SUBDIR.
4. add entry to apps/plugins/viewers.config
(in format: file_extension,viewer/imageviewer) so that the file with specified
file extension will be opened by image viewer plugin.
if the decoder is supported by particular targets, surround it with same #if
directive in SUBDIR.
5. add entry to apps/plugins/CATEGORIES (in format: decoder_name,viewer) so
that the build file is copied to viewers directory.
DON'T surround this with #if directive.
notes:
if you need to use greylib functions to draw image, add the functions to
struct imgdec_api just like gray_bitmap_part because GREY_INFO_STRUCT is
declared in imageviewer and is not available from the decoder.